Many communication systems provide speech communication services, i.e., convey speech between users. The conveyed speech is often compressed using a suitable speech encoding scheme before it is transmitted. Some communication protocols deploy multiple different speech encoding schemes. For example, the Global System for Mobile communications (GSM) standards, the Universal Mobile Telecommunications Service (UMTS) standards and the GSM EDGE Radio Access network (GERAN) standards use a set of speech encoding schemes referred to as Adaptive Multi-Rate (AMR). AMR is defined, for example, in 3rd Generation Partnership Project (3GPP) Technical Specification 26.071, entitled “Technical Specification Group Services and System Aspects; Mandatory Speech CODEC Speech Processing Functions; AMR Speech CODEC; General Description (Release 6),” (3GPP TS 26.071), version 6.0.0., December, 2004, and in 3GPP Technical Specification 45.009, entitled “Technical Specification Group GSM/EDGE Radio Access Network; Link Adaptation (Release 6),” (3GPP TS 45.009), version 6.2.0, June, 2005, which are incorporated herein by reference.
In some communication protocols, the appropriate speech encoding scheme is selected based on the channel conditions between the transmitter and the receiver. For example, section 3.3.1 of 3GPP TS 45.009, cited above, proposes the use of Carrier to Interference Ratio (CIR) as a criterion for selecting an appropriate AMR encoding scheme.